The present invention relates to the manufacture of electronic devices. More particularly, the invention provides a device for polishing a film of material of an article such as a semiconductor wafer. In an exemplary embodiment, the present invention provides an improved substrate support for the manufacture of semiconductor integrated circuits. However, it will be recognized that the invention has a wider range of applicability; it can also be applied to flat panel displays, hard disks, raw wafers, MEMS wafers, and other objects that require a high degree of planarity.
The fabrication of integrated circuit devices often begins by producing semiconductor wafers cut from an ingot of single crystal silicon which is formed by pulling a seed from a silicon melt rotating in a crucible. The ingot is then sliced into individual wafers using a diamond cutting blade. Following the cutting operation, at least one surface (process surface) of the wafer is polished to a relatively flat, scratch-free surface. The polished surface area of the wafer is first subdivided into a plurality of die locations at which integrated circuits (IC) are subsequently formed. A series of wafer masking and processing steps are used to fabricate each IC. Thereafter, the individual dice are cut or scribed from the wafer and individually packaged and tested to complete the device manufacture process.
During IC manufacturing, the various masking and processing steps typically result in the formation of topographical irregularities on the wafer surface. For example, topographical surface irregularities are created after metallization, which includes a sequence of blanketing the wafer surface with a conductive metal layer and then etching away unwanted portions of the blanket metal layer to form a metallization interconnect pattern on each IC. This problem is exacerbated by the use of multilevel interconnects.
A common surface irregularity in a semiconductor wafer is known as a step. A step is the resulting height differential between the metal interconnect and the wafer surface where the metal has been removed. A typical VLSI chip on which a first metallization layer has been defined may contain several million steps, and the whole wafer may contain several hundred ICs.
Consequently, maintaining wafer surface planarity during fabrication is important. Photolithographic processes are typically pushed close to the limit of resolution in order to create maximum circuit density. Typical device geometries call for line widths on the order of 0.5 xcexcm. Since these geometries are photolithographically produced, it is important that the wafer surface be highly planar in order to accurately focus the illumination radiation at a single plane of focus to achieve precise imaging over the entire surface of the wafer. A wafer surface that is not sufficiently planar, will result in structures that are poorly defined, with the circuits either being nonfunctional or, at best, exhibiting less than optimum performance. To alleviate these problems, the wafer is xe2x80x9cplanarizedxe2x80x9d at various points in the process to minimize non-planar topography and its adverse effects. As additional levels are added to multilevel-interconnection schemes and circuit features are scaled to submicron dimensions, the required degree of planarization increases. As circuit dimensions are reduced, interconnect levels must be globally planarized to produce a reliable, high density device. Planarization can be implemented in either the conductor or the dielectric layers.
In order to achieve the degree of planarity required to produce high density integrated circuits, chemical-mechanical planarization processes (xe2x80x9cCMPxe2x80x9d) are being employed with increasing frequency. A conventional rotational CMP apparatus includes a wafer carrier for holding a semiconductor wafer. A soft, resilient pad is typically placed between the wafer carrier and the wafer, and the wafer is generally held against the resilient pad by a partial vacuum. The wafer carrier is designed to be continuously rotated by a drive motor. In addition, the wafer carrier typically is also designed for transverse movement. The rotational and transverse movement is intended to reduce variability in material removal rates over the surface of the wafer. The apparatus further includes a rotating platen on which is mounted a polishing pad. The platen is relatively large in comparison to the wafer, so that during the CMP process, the wafer may be moved across the surface of the polishing pad by the wafer carrier. A polishing slurry containing chemically-reactive solution, in which are suspended abrasive particles, is deposited through a supply tube onto the surface of the polishing pad.
CMP is advantageous because it can be performed in one step, in contrast to past planarization techniques which are complex, involving multiple steps. Moreover, CMP has been demonstrated to maintain high material removal rates of high surface features and low removal rates of low surface features, thus allowing for uniform planarization. CMP can also be used to remove different layers of material and various surface defects. CMP thus can improve the quality and reliability of the ICs formed on the wafer.
Chemical-mechanical planarization is a well developed planarization technique. The underlying chemistry and physics of the method is understood. However, it is commonly accepted that it still remains very difficult to obtain smooth results near the center of the wafer. The result is a planarized wafer whose center region may or may not be suitable for subsequent processing. Sometimes, therefore, it is not possible to fully utilize the entire surface of the wafer. This reduces yield and subsequently increases the per-chip manufacturing cost. Ultimately, the consumer suffers from higher prices.
It is therefore desirable to improve the useful surface of a semiconductor wafer to increase chip yield. What is needed is an improvement of the CMP technique to improve the degree of global planarity that can be achieved using CMP.
The present invention achieves these benefits in the context of known process technology and known techniques in the art. The present invention provides an improved planarization or polishing apparatus for chemical mechanical planarization and other polishing such as metal polishing and optical polishing. Specifically, a drive assembly having a projected gimbal point substantially on the surface of the workpiece to be polished provides improved polishing by self-aligning the polishing surface of the polishing pad on the workpiece surface and eliminating cocking motion of the workpiece relative to the polishing pad. The polishing pad has a hard backing material for improved planarity. As used herein, a hard polishing pad refers to a polishing pad with a hard backing material. For instance, the polishing pad may be connected to and supported by a hard puck.
In accordance with an aspect of the present invention, an apparatus for polishing an object comprises a pad having a polishing surface to be placed on a target surface of the object to be polished. A pad drive member is connected to the pad to move the pad relative to the object to change a position of the polishing surface of the pad on the target surface of the object. The pad comprises a backing material having a modulus of elasticity of at least about 300,000 psi.
In specific embodiments, the pad includes grooves on the polishing surface. The pad has a thickness between about 0.05 and about 0.1 inch. The pad backing material comprises a ceramic material. A compliant layer may be disposed between the pad and the pad drive member. The compliant layer comprises an elastomeric material.
In some embodiments, a drive support is movably coupled with the pad drive member to support the pad drive member for rotation relative to the drive support around a pivot point which is disposed substantially on the target surface of the object during polishing. The pad drive member includes a convex spherical surface centered about the pivot point, and the drive support includes a concave spherical surface rotatably coupled with the convex spherical surface of the pad drive member. The pivot point is spaced from the target surface by a distance less than about 0.1 times, more desirably about 0.02 times, a diameter of the polishing surface during polishing. In a specific embodiment, the pivot point is disposed below the target surface of the object during polishing.
In specific embodiments, the drive support comprises an inner support member and an outer support member. The inner support member is rotatably coupled with the pad drive member to rotate relative to the pad drive member about a first rotational axis extending through the pivot point and being parallel to the polishing surface. The outer support member is rotatably coupled with the inner support member to rotate relative to the inner support member about a second rotational axis extending through the pivot point and being parallel to the polishing surface and nonparallel to the first rotational axis. The first rotational axis is perpendicular to the second rotational axis. The pad drive member includes at least one guide pin each extending into a guide slot provided in the inner support member. The guide slot permits the guide pin to move relative thereto only in rotation about the first rotational axis. The inner support member includes at least one guide pin each extending into a guide slot provided in the outer support member. The guide slot permits the guide pin to move relative thereto only in rotation about the second rotational axis. The drive support is coupled with the pad drive member to move together in rotation around an axis extending through the pivot point and perpendicular to the polishing surface.
A back support may be configured to support a back surface of the object opposite from the pad. The back support is rotatably coupled with a back support frame to rotate about a back pivot point which is disposed substantially on the back surface of the object during polishing. The back support includes a convex spherical surface centered about the back pivot point and the back support frame includes a concave spherical surface rotatably coupled with the convex spherical surface of the back support.
In accordance with another aspect of the invention, an apparatus for polishing an object comprises a pad having a polishing surface to be placed on a target surface of the object to be polished. The pad comprises a backing material having a modulus of elasticity of at least about 300,000 psi. A pad drive member is connected to the pad to move the pad relative to the object to change a position of the polishing surface of the pad on the target surface of the object. A first drive support is movably coupled with the pad drive member to support the pad drive member to rotate relative to the first drive support around a first rotational axis which is parallel to the polishing surface and disposed substantially on the target surface of the object during polishing. A second drive support is movably coupled with the first drive support to support the first drive support to rotate relative to the second drive support around a second rotational axis which is parallel to the polishing surface, nonparallel to the first rotational axis, and disposed substantially on the target surface of the object during polishing.
In some embodiments, the first rotational axis is perpendicular to the second rotational axis. The first rotational axis and the second rotational axis intersect at a gimbal point which is disposed substantially on the target surface of the object during polishing. The pad drive member includes a convex spherical surface. The first drive support includes a concave spherical surface rotatably coupled with the convex spherical surface of the pad drive member. The first drive support includes a convex spherical surface, and the second drive support includes a concave spherical surface rotatably coupled with the convex spherical surface of the first drive support. The pad drive member is rotatable relative to the first drive support only around the first rotational axis, and the first drive support is rotatable relative to the second drive support only around the second rotational axis.